I have used the Berry bullets and they are fine. They cost just a little more than cast lead but are easier to work with as you are not fighting the lube that is on the finished round. I have fired a lot of cast lead in my G17 and G21sf. While this is not recommended by Glock, I find my pistols do not show more leading than my non-Glock pistols.
The most accurate load I have found for my G21sf is the Zero 200gr lead SWC with 6.3 grains of Universal at OAL of 1.250.
I do clean my Glock barrels after every range shoot, as the lead can build up in any firearm and increase pressure.